The present invention relates to airless spraying apparatus for liquid such as paint and, more particularly, to a safety airless spray tip having an integral guard for preventing accidental human injection of a liquid being sprayed.
The airless spraying apparatus of concern herein hydraulically atomizes the liquid being sprayed and, accordingly, relatively high pressures (1,500 to 3,000 psi) capable of human injection are encountered. The emitted spray stream has a "flat fan" shape and it is of sufficient integrity to result in the injection of human skin at locations immediately adjacent the spray tip opening, the downstream atomization of the spray serving to thereafter break up the liquid to a degree which prohibits injection. Thus, a zone of potential injection exists in the emitted spray at the spray tip opening and persists downstream for a relatively short distance. The extent of the zone will vary in accordance with the operating pressure and kinetic energy of the emitted spray as well as the area of the spray opening. It has been found in most commercial and industrial airless spray applications that the zone of potential injection extends for a distance no greater than about 3/8 of an inch as measured from the spray opening. However, it is possible in some very high volume or high energy applications with a narrow spray angle for the zone of potential injection to be as long as 5/8 of an inch or longer.
The prior art discloses a number of protective guard structures for preventing human injection by airless spray apparatus. U.S. Pat. Nos. 3,952,955; 3,963,180 and 4,025,045 disclose relatively large, enclosure type structures characterized by continuous walls which surround or substantially surround the emitted spray adjacent the spray tip for a distance sufficient to prevent injection. These guards are removably mounted on the spray tip retainer nut or entrapped between the retainer nut and the spray tip. In addition, there is presently available an enclosure type guard which is permanently mounted on the retainer nut. This latter guard has a generally cylindrical configuration including a diametrically extending slot having outwardly tapering walls in the downstream direction to provide a spray-receiving region similar to that of the guard in U.S. Pat. No. 3,952,955.
The foregoing enclosure type guards are not satisfactory for a number of reasons. In some cases, the use of the guard requires a specially manufactured or modified retainer nut for purposes of mounting the guard and, frequently, the guard and/or the retainer nut must also include means to orient the guard with the spray tip and the emitted flat fan spray. Thus, such guards are not directly usable in conventional spray apparatus without specially fabricated mounting devices. Further, such guards typically involve additional assembly steps and may be inadvertently omitted when the spray tip is removed for cleaning or replacement. The relatively large, continuous walls of the enclosure type guards also tend to collect liquid or paint being sprayed and to adversely affect the flow of atomization air to the emitted spray. These latter deficiencies have been found sufficiently severe in the enclosure type guard presently being marketed to cause operators to intentionally and destructively remove the guards even though the guards are intended to be permanently mounted to the retainer nut.
U.S. Pat. No. 4,036,438 discloses an open frame type guard having a spray encircling barrier for use with cone-shaped sprays. The guard is removably mounted by means of entrapment between a spray nozzle and a mounting nut or by means of a depending coil spring resiliently engaging the outer periphery of the spray nozzle. The removable mounting arrangement of this guard gives rise to the same deficiencies as noted above with respect to the enclosure type guards, and it is not intended for use with flat fan sprays as contemplated herein.